Mag Ext / BBL Clamp Type HW
The Nordic Components stuff is beautifully machined and detailed. Top quality. None better that I have seen. I have a bbl/mag ext clamp on my HD 1100.
Scattergun Tech/Wilson mag ext is built like a brick you-know-what, but still required a mag ext/bbl clamp. I have one on my HD 1100.
Choate is not as pretty as either of the above, but is perfectly serviceable. I used Choate HW on a police trade-in 870 and it works great (mag ext, bbl/mag clamp, fore end with picatinny rail).
If you want it pretty and functional, go Nordic and/or Wilson. If you just want function, Choate will do the trick.
I prefer an 18" bbl, so went with +2 mag extenders.
Stock & Fore-end
If function is all you desire in a fore-end, Choate produces a synthetic one with a picatinny rail that mounts at 3/6/9 o'clock to mount a combat light like the TLR-3 or TLR-1 (my first & second suggested combat lights).
Remington parts store sells several different stock sets and stocks by their own selves as well as a spacer set that would be a nice way to tune the fit.
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My Rem 870 with Choate HW:
My Rem 1100 with Scattergun Tech / Wilson mag ext before Nordic clamp:
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Have fun & good luck.